1. Field of the Invention
This invention relates to a chip antenna used for electronic equipment with a communication function, such as cellular phone and personal digital assistant equipment, as well as an antenna device and communication equipment using such chip antenna.
2. Description of the Related Art
The frequency range in communication equipment, such as a cellular phone and wireless LAN, ranges from hundreds of MHz to several GHz. It is required for this frequency range to be wide and for the efficiency in this range to be high. Therefore, the antenna used for this communication equipment also needs to have high gain in this frequency range and to be small and thin. In the ground digital broadcasting started in recent years, the frequency range in the television broadcasting in Japan is 470 MHz-770 MHz, for example. When it corresponds to all the channels, it is required that this antenna can receive such a wide frequency range. As digital broadcasting, 180 MHz-210 MHz band is used in South Korea and 470 MHz-890 MHz band is used in Europe. Therefore, a small antenna which can be carried in communication equipment, such as a personal digital assistant, is desired to be usable in a frequency range of 180 MHz or more. It is especially demanded to be small and also thin.
Conventionally, a chip antenna using dielectric ceramics as a small antenna suitable for mobile communications has been offered (for example, see Japanese Patent No. H10-145123). When setting frequency constant, miniaturization of a chip antenna can be attained by using dielectrics with a higher dielectric constant. In art given in this document, the wavelength is shortened by providing a meander shaped electrode. Moreover, the antenna aiming at miniaturization is also proposed by shortening a wavelength 1/(∈r·μr)1/2 times using the magnetic material with large relative permittivity ∈r and large relative magnetic permeability μr (for example, see Japanese Patent No. S49-40046).
Moreover, for example with a small liquid crystal television, the whip antenna using the metal stick is generally used as a receiving antenna currently used for television or radio. This system is beginning to be used also for the cellular phone with television function. Furthermore, the electric wire, which is a part of earphones used with a cellular phone, may be used as a receiving antenna of radio or television.
Although the above-mentioned dielectric chip antenna is advantageous for a miniaturization and thinning, there are the following problems to make bandwidth of a frequency range wide. For example, when using a helical-type radiation electrode as an electrode, if the number of turns increases, the capacitance between electric wires will increase and Q value will become high. Therefore, bandwidth becomes narrow and it becomes difficult to apply to uses, such as ground digital broadcasting for which wide bandwidth is required. Also using another type of electrode, there was a problem that bandwidth could not be made wide because of the capacity between electric wires when patterned electrodes, such as a meander shaped electrode, are formed, or when many electrodes are exposed to the inside of a base substance, or the exterior, etc. Even if it is the antenna using a magnetic material indicated in the 2nd documents, a miniaturization or widening of the bandwidth cannot be achieved, unless it suppresses formation of a capacity component in this structure and an inductance component is formed effectively. Since the above-mentioned whip antenna was large, in order to store it to small apparatus, such as a cellular phone, complicated mechanism is needed. There was a problem of being easy to break when this apparatus falls. With the above-mentioned earphone type antenna, when using radio and television, the reliability of an antenna falls by repeating attachment and detachment. When the electric wire used as an antenna contacts a human body, a gain and sensitivity may deteriorate remarkably.
Therefore, the present invention aims at providing a chip antenna, an antenna device, and communication equipment suitable for making miniaturization and bandwidth of a frequency band wide.